Introduction to Portlet Development
by Jeff Robinson
In the beginning there was the static, immovable web page, always displaying reliably within your (insert your vendor name here) browser. Then came the urgency for making web pages more interactive and the content dynamic. After several different approaches and evolutions, we now have what is widely known as Web 2.0. Part of the technology behind Web 2.0 is the development specification for portlets.
To understand portlets, you have to first know about servlets. Servlets are Java class components that execute on the server per web-page request and which returns the reply back as a recognizable browser response. (Go to this link, Java Servlet Technology, to find out more about servlets.) Portlets, therefore, are what you get when you sub-divide this request/response system among several different Java class components. In other words, instead of just a single servlet being responsible for handling the response, multiple little servlets (or portlets) become responsible for handling the response.
Of course, there are many other things you need to know about how portlets work. For instance, you need to know that another layer of control is added to the server with the use of a special container, known as a Portlet container. This container manages the portlets and ensures that the proper request/response is handled among the portlets. Additionally, there is the Portal layer that encompasses the portlet container, content management, administrative task, etc.
The technical standard for using is embodied in the JSR-168-Portlet Specification document (see link to the PDF below). You should read and understand this specification before proceeding further with your discovery of portlets on the web. A new standard, JSR-286, is also available which remedies most of the deficiencies of the the prior specification.
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